One printing machine of the type to which the present invention relates has been described in "Technisches Jahrbuch fur den Offsetdrucke," 1979, pp. 24 and 25, published by ROLAND Offsetmaschinenfabrik Faber & Schleicher AG, Offenbach, Fed. Rep. Germany ("Technical Yearbook for the Offset Printer"). As there shown, two printing stations have a sheet supplied thereto with a sheet reversing system interposed. The sheet reversing system is so constructed that the leading edge of a sheet is held by grippers which are secured to a chain, and guided past an adjacent drum so that the trailing edge can be gripped by the drum. After opening of the grippers on the leading edge, the previously trailing edge then becomes the leading edge and is carried in that position to the next printing station. Adjusting such a printing machine for prime and verso printing requires more time than setting-up such a machine for prime printing only. Additional apparatus must be provided to prevent excessive scrap production, such as use of compressed air, air nozzles, or suction air at suitable locations, since the sheets tend to smear as they are being turned or reversed. Further, each one of the sheets must have a strip which is free from print not only along the leading edge but also along the trailing edge. The trailing edge strip must match that of the leading edge since, after reversal, that one becomes the leading edge, on which grippers must be capable of holding the sheet. The format of the sheet is not as efficiently used in prime and verso printing as when only single side multiple color printing is applied thereto.
Printing machines arranged for prime and verso printing are also disclosed in the book by Walenski, "Einfuhrung in de Offsetdruck," p. 155 ("Introduction to Offset Printing"). The sheet is printed on both sides by being passed between two rubber blanket cylinders. Such machines can also be used, basically, for single-side single-color printing. This requires disconnection of one of the printing systems including the associated inker and damper. If the proportion of the prime-and-verso printing jobs is small in relation to the printing jobs requiring only prime printing, then such a machine is not utilized effectively during a large portion of its operating time.